With the rapid advances in communication technologies, children are increasingly exposed to the radiofrequency (RF) fields starting from a very early age. As cellular telephones are a new, but increasingly common source of a relatively high RF fields, concerns are increasing that this technology could have negative health effects. Investigation need to be initiated immediately while there are still some populations with no or low exposure. In line with the NIEHS's mission to promote the public's right to a healthy environment, the aim of this proposed research is to understand whether exposure to cellular telephones in childhood can have effects on the central nervous system and whether children might be particularly at risk. The Danish National Birth Cohort (DNBC) represents a unique resource, which will allow us to efficiently evaluate whether exposures [in children] lead to behavioral and developmental effects. The cohort consists of over 100,000 Danish children, who were born between 1996 and 2002. Detailed information on lifestyle factors, dietary habits and environmental exposures has been collected. When these children reached the age of seven, we began to ask about current use of cell phones by children. Our results among 10% of the children suggest that cell phone exposure might be related to behavioral and developmental problems. These findings need to be replicated for the rest of the cohort, [and to evaluate if our findings are limited to "early users", who might be different from the rest of the population. Also, several additional potential confounders have been suggested, and we plan re-analysis adjusting for these factors.] We also propose to investigate other central-nervous system-related outcomes such as seizures, autism, migraines, and sleep disturbances. The proposed novel project is the first large scale study to examine health effects of cell phone use early in life. Given that there are over two billion subscribers worldwide and that children are beginning to use cell phones at earlier ages, studies of children have been determined to be of the highest priority by both national and international organizations, including the World Health Organization and National Academy of Sciences. Children may be at greater risk because: 1) their exposure to the RF might be higher due to differences in the anatomy, tissue conductivity and other factors;2) they might be more susceptible due to the developing organ and tissue systems, particularly of the nervous system;and 3) children born in the last decade are part of a unique population that will have lifelong cell phone exposure. [Our preliminary results have results have received a widespread scientific and media attention. Several issues have been raised post publication.] Here we propose to address these issues and thus to significantly advance our knowledge on health effects of RF field exposure in a potentially vulnerable population and contribute to the risk assessment and policy development of this ubiquitous and rapidly increasing exposure. We believe such a study is urgently needed and at present it can only be done using data sources outside the U.S. PUBLIC HEALTH RELEVANCE: To date potential health effects of cell phone use [in children] have not been adequately examined. As this exposure is extremely prevalent, even very small effects of cell phone exposure could have a large public health impact. [We have reported an important result which needs replication: further information will have immediate policy implications.] If our findings are confirmed reducing exposure in this very vulnerable population is easily achievable.